Industrial vehicle

ABSTRACT

An industrial vehicle which is equipped with an engine and having an Eco-mode in which torque of the engine is restricted includes an accelerator, an accelerator opening detector that detects an opening of the accelerator, a vehicle speed detector that detects a speed of the vehicle, an engine speed detector that detects a speed of the engine, and a torque restriction releasing unit which, when the torque of the engine is restricted, if conditions that the opening of the accelerator detected by the accelerator opening detector is a first predetermined value or greater, that the vehicle speed detected by the vehicle speed detector is a second predetermined value or smaller and that the engine speed detected by the engine speed detector is a third predetermined value or smaller are satisfied, releases the torque restriction.

BACKGROUND OF THE INVENTION

The present invention relates to an engine-powered industrial vehicle.

A hybrid vehicle equipped with an Eco-mode (an economy mode) for thepurpose of improving fuel efficiency has been proposed. By pressing theEco-mode button, the vehicle is placed in the Eco-mode in which theoutput torque of the vehicle is restricted for energy saving, whichleads to an efficient driving of an engine. Such vehicle is disclosed inJapanese Unexamined Patent Application Publication No. 2008-105532.

This Publication discloses a hybrid vehicle in which, in the economymode, torque is supplemented by the motor while the engine is beingdriven efficiently so as to maintain the vehicle performance forimprovement of fuel efficiency. Unlike such a hybrid vehicle, in anengine type industrial vehicle having no traction motor, specifically ina forklift truck, simply operating the forklift truck in the Eco-mode soas to improve the fuel efficiency by restricting the torque may causesome troubles to some operations of the forklift trucks due to shortageof torque. For example, an industrial vehicle carrying a heavy load maynot be able to climb a slope in a working site, which is supposed to beclimbable, due to insufficient hill-climbing performance or insufficientengine torque.

The present invention is directed to providing an industrial vehiclecapable of providing a torque restriction control in an Eco-mode thatpermits both improvement of fuel efficiency and maximization of vehicleperformance.

SUMMARY OF THE INVENTION

The present invention is directed to providing an industrial vehiclewhich is equipped with an engine and having an Eco-mode in which torqueof the engine is restricted. The industrial vehicle includes anaccelerator, an accelerator opening detector that detects an opening ofthe accelerator, a vehicle speed detector that detects a speed of thevehicle, an engine speed detector that detects a speed of the engine,and a torque restriction releasing unit which, when the torque of theengine is restricted, if conditions that the opening of the acceleratordetected by the accelerator opening detector is a first predeterminedvalue or greater, that the vehicle speed detected by the vehicle speeddetector is a second predetermined value or smaller and that the enginespeed detected by the engine speed detector is a third predeterminedvalue or smaller are satisfied, releases the torque restriction.

In accordance with an aspect of the present invention, when the torqueis restricted, if the conditions that the opening of the acceleratordetected by the accelerator opening detector is the first predeterminedvalue or greater, that the vehicle speed detected by the vehicle speeddetector is the second predetermined value or smaller and that theengine speed detected by the engine speed detector is the thirdpredetermined value or smaller are satisfied, the torque restriction isreleased. Therefore, the torque restriction control is performed in sucha way that improvement of fuel efficiency and maximization of vehicleperformance are achieved simultaneously.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The inventiontogether with objects and advantages thereof, may best be understood byreference to the following description of the embodiments together withthe accompanying drawings in which:

FIG. 1 is a schematic view showing an overall configuration of aforklift truck according to an embodiment of the present invention;

FIG. 2A is a table explaining the conditions for releasing a torquerestriction in the forklift truck of FIG. 1;

FIG. 2B is a table for explaining the conditions for resuming the torquerestriction in the forklift truck of FIG. 1; and

FIG. 3 is a timing chart showing the operation of the forklift truck ofFIG. 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following will describe an embodiment of an industrial vehicleaccording to the present invention with reference to the drawings.

Referring to FIG. 1, numeral 10 designates a forklift truck including aloading unit 11. The loading unit 11 has a multi-stage mast assembly 14including a pair of right and left outer masts 12 and a pair of innermasts 13. Each outer mast 12 is connected to a hydraulic tilt cylinder15 and each inner mast 13 is connected to a hydraulic lift cylinder 16.The mast assembly 14 is tiltable in the forward and backward directionsof the forklift truck 10 in response to hydraulic oil flowing into andout of the tilt cylinders 15. The inner masts 13 are movable upward anddownward in the vertical direction of the forklift truck 10 in responseto hydraulic oil flowing into and out of the lift cylinders 16. Forks 18are mounted to the inner masts 13 via lift brackets 17. The inner masts13 are raised and lowered along the outer masts 12 by the operation ofthe lift cylinders 16 and the forks 18 and the lift brackets 17 andmoved accordingly.

The forklift truck 10 includes an engine 19 that serves as a drivesource for traveling and loading operation of the forklift truck 10, ahydraulic pump 20 that is driven by the engine 19, a hydraulic mechanism21 to which hydraulic oil discharged from the hydraulic pump 20 issupplied and a power transmission mechanism 22. Output of the engine 19is converted into the drive force for traveling of the forklift truck 10and also the drive force for operating the tilt cylinders 15 and thelift cylinders 16 for loading operations.

The hydraulic pump 20 is driven to pump hydraulic oil in an oil tank 23.The pumped oil is then supplied to the tilt cylinders 15 and the liftcylinders 16 through the hydraulic mechanism 21 and at the same time,the hydraulic oil discharged from the tilt cylinders 15 and the liftcylinders 16 is returned to the oil tank 23 through the hydraulicmechanism 21. The hydraulic mechanism 21 includes an electromagneticcontrol valve (not shown) that controls supply and discharge of thehydraulic oil flowing into and out of the tilt cylinders 15 and the liftcylinders 16.

The power transmission mechanism 22 has a mechanism for transmittingpower such as a torque converter or a clutch (neither being shown). Theengine 19 is connected to the power transmission mechanism 22, which isin turn connected to a pair of drive wheels 26 via a differential gear24 and an axle 25 having the drive wheels 26 mounted on the oppositeends thereof. Therefore, the output power of the engine 19 istransmitted to the drive wheels 26 through the power transmissionmechanism 22, the differential gear 24 and the axle 25.

Operation of the tilt cylinders 15 and the lift cylinders 16 isaccomplished by operating a loading lever 27 which actually includes atilt lever and a lift lever. Operation of the loading lever 27 isdetected by a loading lever sensor 28. Acceleration of the forklifttruck 10 is accomplished by depressing an accelerator pedal 29. Thedepression of the accelerator pedal 29 or the opening of the acceleratorpedal 29 is detected by an accelerator opening sensor 30. An Eco-modeswitch 31 is provided at a position adjacent to the driver's seat of theforklift truck 10.

The forklift truck 10 further includes a vehicle control unit 32. Thevehicle control unit 32 is electrically connected to the loading leversensor 28, the accelerator opening sensor 30, the Eco-mode switch 31 anda vehicle speed sensor 33 as the vehicle speed detector of the presentinvention. Based on the detection signals from the sensors 28, 30, 33and the switch 31, the vehicle control unit 32 determines the operationof the loading lever 27, the depression of the accelerator pedal 29 (orthe opening of the accelerator 29), the vehicle speed and the Eco-modeswitch 31 (ON or OFF position). For a desired loading operation, thevehicle control unit 32 controls the hydraulic mechanism 21 thereby tocontrol the flow of hydraulic oil into and out from the tilt cylinders15 and the lift cylinders 16. Specifically, for example, the forklifttruck driver operates the tilt cylinders 15 and the lift cylinders 16 byoperating the loading lever 27 (the tilt lever or the lift lever) whiledepressing the accelerator pedal 29.

The vehicle control unit 32 is connected to an engine control unit 34that controls the engine 19. The engine 19 has an engine speed sensor 35that detects the speed of the engine 19. The engine speed sensor 35 asthe engine speed detector of the present invention generates rotationdetection signals to the engine control unit 34. The vehicle controlunit 32 detects the speed of the engine 19 based on the signal from theengine control unit 34.

The vehicle control unit 32 generates to the engine control unit 34 aninstruction signal to control the speed of the engine 19. Specifically,for example, the speed of the engine 19 is controlled according to thedepression of the accelerator pedal 29. The vehicle control unit 32 alsogenerates to the engine control unit 34 a torque restriction instructionsignal according to the position of the Eco-mode switch 31. Upon receiptof the torque restriction instruction signal, the engine control unit 34controls the engine 19 so as to restrict its output torque in theEco-mode of operation.

The following will describe the operation of the forklift tuck 10.

The vehicle control unit 32 changes the value for the torque restrictionaccording to the ON or OFF position of the Eco-mode switch 31 and asignal representing the torque restriction value is issued to the enginecontrol unit 34. In normal mode of operation, the engine 19 generates afull torque corresponding to the current opening of the acceleratorpedal 29. In the Eco-mode of operation, on the other hand, the outputtorque of the engine 19 is restricted and the engine 19 generates atorque that is reduced to approximately 80 percent of full torque in thenormal mode, thereby suppressing the consumption of fuel by the engine19. It is to be noted that an optimum value for the torque restrictionis previously determined taking the maximum load capacity, thespecifications of the engine 19 and the nature of the task to be takenby the forklift truck 10 into account.

The vehicle control unit 32 determines the opening of the acceleratorpedal 29, the operated position of the loading lever 27, the vehiclespeed and the speed of the engine 19.

As shown in FIG. 2A, the conditions A1, A2, A3 and A4 are previously setas the conditions for releasing the torque restriction.

In the table of FIG. 2A, the condition A1 is a condition associated withthe opening of the accelerator pedal 29 in releasing the torquerestriction. The condition Al requires that the opening of theaccelerator pedal 29 be a first predetermined value XA or greater. Thevalue XA corresponds to the full opening of the accelerator pedal 29. Inview of a free play of the accelerator pedal 29, the value XA may be 85%to 90% of the opening of the accelerator pedal 29 which is fully, or100%, depressed.

The condition A2 in the table of FIG. 2 is a condition associated withthe vehicle speed of the forklift truck 10 in releasing the torquerestriction. The condition A2 requires that the vehicle speed be asecond predetermined value YA or smaller. The value YA is a secondpredetermined value used for determining whether or not the vehicle issubstantially at a stop. The reference value for the stop does not needto be 0 km/h representing a complete stop of the forklift truck 10, butis preferably set to approximately 1 to 3 km/h with the accuracy of thevehicle speed sensor 33 taken into account.

The condition A3 in the table of FIG. 2 is a condition associated withthe speed of the engine 19 in releasing the torque restriction. Thecondition A3 requires that the speed of the engine 19 be a thirdpredetermined value Z or smaller. The value Z represents a maximumengine speed or the number of rotations (NMR) of the engine 19 operatingunder no load. Actually, the value Z is a value which is obtained bysubtracting a predetermined value (for example, 100 rpm) from the NMRwith an error between the instruction value of engine speed in a dieselengine and the actual engine speed taken into account.

The condition A4 in the table of FIG. 2 is a condition associated withthe operation of the forklift truck 10. The condition A4 requires thatthe forklift truck 10 be not in loading operation. Determination of thiscondition A4 may be accomplished by the detection of the operation ofthe loading lever 27.

Referring to FIG. 2B, the conditions B1 and B2 are previously set as theconditions for resuming the torque restriction after it has been oncereleased (resuming conditions).

The condition B1 shown in FIG. 2 is a condition associated with theopening of the accelerator pedal 29 in resuming the torque restriction.The condition B1 requires that the opening of the accelerator pedal 29be a fourth predetermined valued XB or smaller. The value XB correspondsto the opening of the accelerator pedal 29 other than the full openingof the accelerator pedal 29, e.g. the position where the acceleratorpedal 29 is released from its fully depressed position. Therefore, thevalue XB in the condition B1 is smaller than the value XA in thecondition A1. For the above released condition of the accelerator pedal29 to be detected surely, the value XB is set to approximately 50% ofthe full opening of the accelerator pedal 29.

The condition B2 shown in FIG. 2 is a condition associated with thevehicle speed of the forklift truck 10 in resuming the torquerestriction. The condition B2 requires the vehicle speed to once reachor exceed a fifth predetermined value YB and then decreases to or belowthe second predetermined value YA. The value YB is previously set toapproximately 1 to 5 km/h as the reference value for determining whetheror not the forklift truck 10 is traveling by the output power of theengine 19 transmitted through the power transmission mechanism 22.Furthermore, the value YA is a previously set value for determiningbased on the vehicle speed that operation of stopping the forklift truck10 is made after the vehicle speed once reached or exceeded the fifthpredetermined value YB. Since a forklift truck is generally operatedcontinuously without being completely stopped between tasks, asdescribed earlier, the value YA is not set to 0 km/h representing acomplete stop of the forklift truck 10, but to approximately 1 to 3 km/hwith the accuracy of the vehicle speed sensor 33 taken into account.

It is to be noted that the respective predetermined values for theopening of the accelerator pedal 29 and the vehicle speed are specifiedfor the reasons described above and have been established previouslythrough experiments conducted based on data such as the maximum loadcapacity of the forklift truck 10 and the characteristics of the engine19 to be mounted on the forklift truck 10.

FIG. 3 is a timing chart explaining the sequence of torque restrictionon the engine 19, transitioning firstly from a state in which the torqueis restricted to be smaller than that in the normal mode of operation(such state hereinafter being referred to as the torque restrictionstate) to a state in which torque is no more restricted (such statehereinafter being referred to as the torque restriction released state),and then again to the torque restriction state.

In the timing chart of FIG. 3, the forklift truck 10 remains in thetorque restriction state until time T1.

When the conditions A1 through A4 in FIG. 2A are satisfied at time T1 inFIG. 3 and this is continued for a predetermined period of time TA, thevehicle control unit 32 as the torque restriction releasing unit of thepresent invention starts reducing the torque restriction gradually attime T2 shown in FIG. 3. Specifically, TA between T1 and T2 is apredetermined period of time during which the torque restrictionreleasing conditions are satisfied.

The predetermined period of time TA is set for the purpose of preventingreleasing of the torque restriction by transient satisfaction of theconditions A1 through A4. Specifically, the period of time TA is set toapproximately 10 to 30 seconds as the value which allows the vehiclespeed of the forklift truck 10 to reach its maximum in traveling on aflat surface. The value TA has been determined previously throughexperiments based on data such as the maximum load capacity of theforklift truck 10 or the characteristics of the engine 19 to be mountedto the forklift truck 10.

Transition from the torque restriction state to the torque restrictionreleased state is performed gradually and the transition to the torquerestriction released state is completed at time T3 in FIG. 3.Specifically, the period of time TB between T2 and T3 is the time duringwhich transition is performed from the torque restriction state to thetorque restriction released state.

Thus, the forklift truck 10 enters the torque restriction releasedstate, so that the forklift truck 10 is supplied with an engine torquerequired for climbing a slope.

The following will describe the operation of the forklift truck 10 morein detail.

It is assumed that the Eco-mode switch 31 of the forklift truck 10 istuned ON by an administrator to restrict the torque and lock theforklift truck 10 in the Eco-mode. Operator of the forklift truck 10 isnot authorized to change mode but allowed only to operate the forklifttruck 10 in the Eco-mode with the torque restriction.

In the case of a diesel engine, the fuel injection is reduced by thetorque restriction and the output torque of the engine 19 is reduced,accordingly. In the case of a gasoline engine, the opening of thethrottle valve and hence the flow of air passing through the throttlevalve is reduced and the output torque of the engine 19 is reduced,accordingly. The output torque of the engine 19 is thus restrictedaccording to the opening of the accelerator pedal 29 and theacceleration performance of the forklift truck 10 is restricted therebyto reduce the fuel consumption of the engine 19.

The vehicle speed or the loading speed may be controlled by adjustingthe torque of the engine 19 (or the speed of the engine 19) throughdepression of the accelerator pedal 29. If the condition A1 (the openingof the accelerator pedal 29 being XA or greater), the condition A2 (thevehicle speed being the second predetermined value YA or smaller) andthe condition A3 (the engine speed being the third predetermined value Zor smaller) are kept satisfied for a predetermined duration of time, itis determined that the forklift truck 10 is unable to climb the slope.

If the condition A1 that the opening of the accelerator pedal 29 is XAor greater, the condition A2 that the vehicle speed is YA or smaller,and the condition A3 that the speed of the engine 19 is Z or smaller,are satisfied for the predetermined period of time, it is determinedthat the forklift truck 10 is traveling with the accelerator pedal 29fully depressed, and if such state is continued for the predeterminedperiod of time TA, the torque restriction is reduced gradually. Forexample, the forklift truck 10 loaded with a heavy load in the Eco-modemay not be able to climb a slope due to insufficient torque. In such acase, however, the forklift truck 10 can climb the slope by releasingthe torque restriction.

The condition A3 is used for determining that the engine 19 is operatingunder a load. Therefore, if the speed of the engine 19 is the thirdpredetermined value Z or smaller (a value obtained by subtracting apredetermined value from the NMR), it is determined that engine racingis not performed. Engine racing refers to running an engine at a highspeed under no load with the accelerator fully depressed and the clutchdisengaged. The racing is performed during an inspection or forwarming-up of a vehicle. The torque is restricted when performing theracing. That is, the racing should preferably be performed in the torquerestriction state.

In other words, when it is determined that the engine speed is less thanthe predetermined value Z (NMR of the engine 19 operating under noload), unexpected releasing of the torque restriction on the engine 19which is then being raced with the forklift truck 10 placed at a stop ona flat surface.

When it is determined that the forklift truck 10 is not in the loadingoperation as in the case that the condition A4 is satisfied, it can beascertained that the forklift truck 10 is operating under a travelingload. In other words, the torque restriction is not released in the casethat the forklift truck 10 is operating under a load associated with theloading operation.

In the period between T2 and T3 in FIG. 3, that is the period duringwhich the torque restriction state is shifted to the torque restrictionreleased state, if the opening of the accelerator pedal 29 becomes zero(accelerator OFF), the forklift truck 10 is returned to the torquerestriction sate.

The following will describe the operation for resuming the torquerestriction.

It is assumed that the forklift truck 10 is in the torque restrictionreleased state in the period of time after time T3 and before time T4 inthe diagram of FIG. 3.

If one of the conditions B1 and B2 shown in FIG. 2B, which are theconditions for resuming torque restriction, is satisfied at time T4 inthe diagram of FIG. 3, the vehicle control unit 32, which serves as thetorque restriction resuming unit of the present invention, operates soas to restrict the torque again in a gradual manner for resumption ofthe torque restriction. The resumption of the torque restriction isperformed gradually over a period of time from time T4 to time T5 atwhich the resumption is completed. Thus, the forklift truck 10 isreturned to the torque restriction state.

By so controlling, the forklift truck 10 returns from the torquerestriction released state to the torque restriction state that enablesimprovement of fuel efficiency.

The following will describe the operation for resuming the torquerestriction more in detail.

In the condition B1, when the accelerator pedal 29 fully depressed inthe condition A1 is released, the output torque of the engine 19 drops,which means that the torque restriction does not need to be released.Thus, the forklift truck 10 returns to the torque restriction state.Specifically, if the condition B1 is satisfied, that is, when theopening of the accelerator pedal 29 is reduced to XB or less, it isdetermined that the torque restriction needs to be resumed.

In the condition B2, an operation being attempted to stop the forklifttruck 10 after the vehicle speed once reached or exceeded thepredetermined value YB constitutes a timing for resuming the torquerestriction. Specifically, when the vehicle speed once reaches orexceeds the fifth predetermined value YB and then decreases to or belowthe predetermined value YA, it is determined that the torque restrictionneeds to be resumed. Accordingly, the torque restriction is enabledagain when the forklift truck 10 is accelerated again.

The above-described embodiment of the industrial vehicle offers thefollowing effects:

(1) When the mode of operation of the forklift truck 10 is locked to theEco-mode and the operator cannot cancel the mode, the forklift truck 10appropriately releases the torque restriction and also resumes thetorque restriction for the purpose of improving the fuel efficiency.Additionally, the detection of the traveling condition and the state ofloading operation of the forklift truck 10 makes possible controlling ofthe torque restriction appropriately in view of the manner of operationthat is specific to a forklift truck. Alternatively, the forklift truck10 may be equipped with an angle gauge that measures a slope. In thepresent embodiment, however, the torque restriction can be controlledwithout such an additional device. Therefore, the improvement of thefuel efficiency of the engine type forklift truck 10 can be accomplishedwith no increase in manufacturing cost. Furthermore, the minimumrequired hill-climbing performance of the forklift truck 10 is ensuredwithout an angle gauge for detecting a slope.

(2) The engine type forklift truck 10 has the accelerator opening sensor30, the vehicle speed sensor 33, the engine speed sensor 35 and thevehicle control unit 32. When the condition that the opening of theaccelerator pedal 29 is the first predetermined value XA or greater andthe condition that the vehicle speed is the second predetermined valueYA or smaller and the condition that the engine speed is the thirdpredetermined value Z or smaller are satisfied while the forklift truck10 is in the torque restriction state, the vehicle control unit 32releases the torque restriction. By so controlling, if the aboveconditions are satisfied while the forklift truck 10 is in the torquerestriction state, the torque restriction is released and the engine 19generates a torque that is required for performing any specificoperation. Releasing the torque restriction according to the vehicleconditions in the Eco-mode operation of the forklift truck 10 makespossible fulfillment of the improved fuel efficiency and the maximumvehicle performance.

(3) After the torque restriction is released, if one of the conditionthat the opening of the accelerator pedal 29 is the fourth predeterminedvalue XB or smaller and the condition that the vehicle speed oncereaches or exceeds the fifth predetermined value YB and then decreasesto or below the second predetermined value YA is satisfied (if one ofthe conditions B1 and B2 in FIG. 2B is satisfied), the torquerestriction is resumed. Such torque restriction controlling makes thetorque restriction to be resumed easily from the torque restrictionreleased state. In other words, the torque restriction becomes effectiveagain according to the state of the forklift truck 10. Therefore, thefuel efficiency can be improved by using the Eco-mode operation of theforklift truck 10.

(4) The resumption of the torque restriction, which is accomplished byfulfillment of the condition B1, that is the opening of the acceleratorpedal 29 being the fourth predetermined value XB or smaller, can be maderapidly.

(5) The torque restriction once released when the vehicle speed in (3)above becomes YA or smaller can be resumed if the vehicle speed becomesYB or greater. The resumption of the torque restriction, which isaccomplished by fulfillment of the condition B2, that is the conditionthat the vehicle speed once reaches or exceeds the fifth predeterminedvalue YB and then accelerating the forklift truck 10.

(6) By providing the condition A4 as the condition for releasing thetorque restriction that the forklift truck 10 is not in loadingoperation, the torque restriction is not released unexpectedly when theforklift truck 10 in the torque restriction state is in loadingoperation, such as raising a heavy load.

(7) In the torque restriction releasing condition A3, the speed of theengine 19 which is the third predetermined value Z or smaller is equalto or smaller than a maximum speed of the engine 19 that is operatingunder no load. Therefore, the torque restriction is not released whenthe engine 19 is operating at a high speed under no load, but isreleased only when the engine 19 is subjected to a load, which helps toimprove the fuel efficiency.

(8) The torque restriction is reduced gradually in releasing of thetorque so that the forklift truck operator will not suffer from anuncomfortable feel.

The present invention is not limited to the above embodiment, but it maybe embodied in various ways as exemplified in the following.

When the torque is restricted, the engine output of the forklift truck10 may be insufficient for pushing or pulling a heavy load (pushingoperation of the lift), as well as in the case of climbing a slope. Insuch case, the torque restriction may be released or resumed accordingto the vehicle conditions that are similar to the torque restrictionreleasing conditions or the torque restriction resuming conditions,respectively, in the above-described embodiment.

The torque restriction control in the above-described embodiment may beapplied to industrial vehicles other than forklift trucks, which areequipped with implements such as a bucket. Furthermore, in the case thatthe torque restriction control is applied to an industrial vehicle suchas a traction vehicle having no loading unit, the condition A4 thatrequires the industrial vehicle not to be in loading operation may beomitted.

The control value of the hydraulic mechanism 21 is of an electromagnetictype and its operation is controlled based on electrical signals fromthe vehicle control unit 32. However, such electromagnetic control valvemay be replaced by a mechanical valve. Specifically, various operationparts may be connected to the control valve so that the open and closedstate is switched by operating such operation parts.

The power transmission mechanism 22 may use either a torque converter ora manual transmission.

What is claimed is:
 1. An industrial vehicle which is equipped with anengine and has an Eco-mode in which torque of the engine is restricted,comprising: an accelerator; an accelerator opening detector that detectsan opening of the accelerator; a vehicle speed detector that detects aspeed of the vehicle; an engine speed detector that detects a speed ofthe engine; and a torque restriction releasing unit which, when thetorque of the engine is restricted, if conditions that the opening ofthe accelerator detected by the accelerator opening detector is a firstpredetermined value or greater, that the vehicle speed detected by thevehicle speed detector is a second predetermined value or smaller andthat the engine speed detected by the engine speed detector is a thirdpredetermined value or smaller are satisfied, releases the torquerestriction.
 2. The industrial vehicle according to claim 1, furthercomprising a torque restriction resuming unit which, after the torquerestriction is released by the torque restriction releasing unit, if oneof a condition that the opening of the accelerator detected by theaccelerator opening detector is a fourth predetermined value or smallerand a condition that the vehicle speed detected by the vehicle speeddetector once reaches or exceeds a fifth predetermined value and thendecreases to or below the second predetermined value is satisfied,resumes the torque restriction.
 3. The industrial vehicle according toclaim 1, wherein the torque restriction releasing unit further comprisesa requirement as the condition for releasing the torque restriction thatthe industrial vehicle is not in loading operation.
 4. The industrialvehicle according to claim 1, wherein the engine speed which is thethird predetermined value or smaller is equal to or smaller than a speedwhich is based on the maximum speed of the engine operating under noload.
 5. The industrial vehicle according to claim 1, wherein the torquerestriction releasing unit gradually reduces the torque restriction.